Many low birth weight infants are at risk of poor growth due to an inability to achieve adequate protein intake. Administration of the amino acid, leucine, stimulates protein synthesis in skeletal muscle of neonates. To determine the effects of enteral supplementation of the leucine metabolite, β-hydroxy-β-methylbutyrate (HMB), on protein synthesis and the regulation of translation initiation and degradation pathways, overnight fasted neonatal pigs were studied immediately (F) or fed 1 of 5 diets for 24 h: low protein (LP), high protein (HP), or LP diet supplemented with 4 (HMB 4), 40 (HMB 40), or 80 (HMB 80) µmol HMB·kg body weight-1·d-1. Cell replication was assessed from nuclear incorporation of BrdU in the longissimus dorsi (LD) muscle and jejunum crypt cells. Protein synthesis rates in LD, gastrocnemius, rhomboideus, and diaphragm muscles, lung, and brain were greater in HMB 80 and HP, and in brain were greater in HMB 40, compared to LP and F groups. Formation of the eIF4E·eIF4G complex and S6K1 and 4EBP1 phosphorylation in LD, gastrocnemius, and rhomboideus muscles were greater in HMB 80 and HP than in LP and F groups. Phosphorylation of eIF2α and eEF2 and expression of SNAT2, LAT1, MURF1, atrogin-1, and LC3-II were unchanged. Numbers of BrdU positive myonuclei in the LD were greater in HMB 80 and HP than in LP and F groups; there were no differences in jejunum. The results suggest that enteral supplementation with HMB increases skeletal muscle protein anabolism in neonates by stimulation of protein synthesis and satellite cell proliferation.
- Amino acid
- Protein metabolism
- Translation initiation
- Copyright © 2016, American Journal of Physiology - Endocrinology and Metabolism